The present invention relates to a solid-state image pickup device and a camera using the same.
With increase of requests for higher image quality and higher-level functions of a camera using a solid-state image pickup device such as a charge-coupled device (CCD) (note that the “camera” as used herein only refers to such a camera using a solid-state image pickup device), the number of pixels of the device is becoming larger. Many of recent-model cameras are equipped with a monitor such as a liquid crystal display for monitoring an object to be imaged.
To monitor an object to be imaged reliably, the frame rate should not be so low. As the monitor, a liquid crystal TV display is often used, and in this case, signals similar to those for normal TV display must be supplied. However, a solid-state image pickup device having a large number of pixels requires a comparatively long time to read all signals from pixels, and therefore cannot output signals at a frame rate of normal TV signals necessary for the monitor. To solve this problem, such a camera is provided with a mode (generally called a monitor mode) in which the number of pixels in the vertical direction, for example, is reduced to enable high-speed readout of signals.
For the monitor mode, adopted generally are a method of simply thinning image data on a solid-state image pickup device and reading the thinned data, a method of mixing only data of the same color and a combination of these methods. Also, Japanese Laid-Open Patent Publication No. 2000-324504 discloses a method for driving a solid-state image pickup device having a large number of pixels and a complementary color filter provided for optoelectronic transducers, in which high-speed, high-sensitivity and high-quality readout is realized.
The color filter used for a solid-state image pickup device is roughly classified into a filter using the primary colors and a filter using complementary colors. It is therefore necessary to construct image processing systems for the primary color filter and the complementary color filter separately.
The configuration and operation of a conventional solid-state image pickup device will be described. FIG. 38 is a plan view showing the configuration of a conventional solid-state image pickup device. The solid-state image pickup device of FIG. 38 includes: a horizontal transfer section 92 driven with two-phase drive pulses H1 and H2; a charge detection section 93; vertical transfer sections 94 driven with six-phase drive pulses V1 to V6; and photodiodes 95. One photodiode 95 corresponds to one pixel. In FIG. 38, only eight pixels vertically and four pixels horizontally are shown for simplification.
FIG. 39 is a cross-sectional view of the horizontal transfer section 92 in FIG. 38, showing a cross section in parallel with the direction of charge transfer in the horizontal transfer section 92. Referring to FIG. 39, the horizontal transfer section 92 includes a p-well B1, an n-type diffusion layer B2, n−-type diffusion layers B3 and electrodes B11 to B14.
The n-type diffusion layer B2, formed on the p-well B1, serves as a transfer channel of the horizontal transfer section 92. The n−-type diffusion layers B3, lower in impurity density than the n-type diffusion layer B2, are formed in the n-type diffusion layer B2. The electrodes B11 to B14, driven with the two-phase drive pulses H1 and H2, are formed on the n-type diffusion layer B2 and the n−-type diffusion layers B3. Charges are transferred leftward as is viewed from FIG. 39 inside the n-type diffusion layer B2, to be detected by the charge detection section 93.
FIG. 40 is a timing chart showing the drive pulses applied to the horizontal transfer section 92 in FIG. 38. The drive pulse H1 is applied to the electrodes B11 and B12 of the horizontal transfer section 92, and the drive pulse H2 is applied to the electrodes B13 and B14 thereof, to enable signal charges in the horizontal transfer section 92 to be transferred in the signal charge transfer direction indicated in FIG. 39.
FIG. 41 is a timing chart showing the waveforms of signals for driving the conventional solid-state image pickup device of FIG. 38. In the conventional solid-state image pickup device, a read pulse having a high voltage (about 15 V) is applied to electrodes (V1, V3, V5 and V6 in FIG. 38) of the vertical transfer sections 94, to read charges from the photodiodes 95 into the vertical transfer sections 94. Also, drive pulses having a voltage lower than the read pulse are applied to the electrodes (V1 to V6 in FIG. 38) of the vertical transfer sections 94, to enable simultaneous transfer of charges corresponding to one row to the horizontal transfer section 92 in one horizontal scanning period.
The charges transferred to the horizontal transfer section 92 are carried to the charge detection section 93 with a clock of about 24.5 MHz, and the charge detection section 93 converts the charges to imaging signals and outputs the results.
A camera provided with the conventional solid-state image pickup device as described above performs processing for pixel reduction such as mixing signal charges read from two pixels each in the vertical transfer sections or thinning the number of rows to a half in a memory outside the solid-state image pickup device, and outputs the resultant image to a monitor such as a liquid crystal display.
However, in the conventional solid-state image pickup device in which signal charges from one row are transferred vertically in one horizontal scanning period, the transfer processing time is long when the number of pixels is large. Even if charges from two pixels are mixed together in the vertical transfer section, it takes long time to output signal charges corresponding to the entire screen, and thus it is impossible to output a sufficient number of frames per unit time.
In addition, in display of a so-called monitor image on a monitor, it is necessary to convert the output signals to interlaced signals and change the frame rate using a memory and the like because the frame rate is low in the conventional solid-state image pickup device. Even if the scanning mode is converted using a memory and the like, display of moving images smooth in motion in real time is unattainable.
In the case that pixels are simply thinned so that 2R-G and 2B-G lines are output line-sequentially by a general drive method for a solid-state image pickup device for realizing the monitor mode described above, equal sampling intervals are not obtainable due to the pattern of a general color filter formed on the solid-state image pickup device, resulting in considerable degradation in image quality and sensitivity. In the case of adopting a method of mixing data of the same color so that 2R-G and 2B-G lines are output line-sequentially, also, the sampling intervals are not equal between a given horizontal line and the next horizontal line, resulting in degradation in image quality.
In the drive method disclosed in Japanese Laid-Open Patent Publication No. 2000-324504 described above, n times of vertical transfer is performed during a horizontal blanking interval in each horizontal scanning period, and at least one time of forward or backward transfer is performed at a time point between the n times of vertical transfer. Therefore, in a general primary color filter array, it is difficult to perform high-speed, high-sensitivity and high-quality readout. If this drive method is adopted for an interlaced scan CCD, the gate structure of the CCD will become very complicate, and thus the number of signals required for the control will increase.
Conventionally, in design of systems of cameras and the like, development is made separately for a system using a solid-state image pickup device having a complementary color filter and a system using a solid-state image pickup device having a primary color filter. It is very inefficient to develop image processing systems separately like this to comply with the respective characteristics of the complementary color filter and the primary color filter. This conventionally makes it difficult to shorten the time required for development of cameras and the like.